Tap changing transformer system



Sept. 20, 1949. N. S JG BERG TAP CHANGING TRANSFORMER SYSTEM Filed July 10, 1946.

Patented Sept. 20, 1949 TAP CHANGING TRANSFORMER SYSTEM Nils Sjiiberg, Stockholm, Sweden, assignor to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application July 10, 1946, Serial No. 682,491 In Sweden August 8, 1945 3 Claims.

In electrical railway drive the speed of the train generally is regulated by a variation of the voltage impressed upon the motors, and this variation is best attained by a regulation on the primary side of the locomotive transformer by its connection according to the desired speed to different tappings on a potentiometer or an autotransformer, which is connected between the trolley-wire and earth.

In order to attain a sufliciently fine regulation of the speed it is necessary to provide the said potentiometer with a large number of tappings and in order to decrease the number of tappings maintaining the number of voltage-steps the potentiometer has been provided with an additional winding coil, which coil during increasing the voltage by changing from one tapping to the next on the potentiometer, has been connected in series with the primary winding of the transformer, This additional winding has then been so dimensioned that the additional voltage generated by it has been parctically the half of the voltage between two adjacent tappings on the potentiometer.

In order to fully utilize the current load ability of the driving motors for the acceleration of the train it is, however, of interest to perform the regulation with voltage steps, which increase with increasing voltage in order to achieve the same increase in current in the motors for each regulating step. The above described arrangement can, however, not be used in the cases when the tappings on the potentiometer are so ar ranged that the voltage steps between adjacent tappings increase with increasing voltage because the voltage generated by the additional winding is constant and thus only can serve for dividing a single voltage interval into equal parts. If, however, the above described arrangement advantageously shall be used for the regulation of a locomotive it is, however, desirable that the additional winding will give a division of all the difierent voltage intervals in two practically equal parts. The present invention has for its object an arrangement, by which this becomes possible, and according to the invention this is achieved thereby that the said additional winding is connected to the transformer fed by the potentiometer instead of to the potentiometer itself so that the voltage over this additional winding will vary in accordance with the voltage impressed upon the transformer. It is also possible to imagine a combination of the two arrangements in that on the potentiometer as well as on the transformer an additional winding is ar- 2 ranged, which windings are connected in series and connected in series with the primary winding of the transformer.

On the accompanying drawing an arrangement of the last mentioned kind is shown, where I designates the trolley-wire and 2 the winding of the potentiometer with the tappings 3 3 and 3 4 designates the locomotive transformer with its primary winding 5 and secondary winding 6 connected to a motor M. On the potentiometer an additional winding '1 is arranged and on the transformer an additional winding 8, which two windings mutually are series-connected and connected to one contact It on the step switch of the potentiometer, whereas the other contact 9 is connected with a switch H, which contains a resistance [2 and four contacts I3, l4, l5 and IS.

The arrangement acts in the following way: It is at first supposed that the contacts 9 and H] are connected with the same tapping on the potentiometer and the contacts l3 and I4 are closed. Then the contact i4 is opened and the contact I5 is closed and I3 is opened so that the voltage from the coils l and 8 over the resistance I2 is added to the voltage before impressed upon the winding 5. Then the circuit breaker I6 is closed so that said voltage without interconnection of the resistance I2 is introduced in the circuit of the winding 5. The voltage, which then is impressed upon the winding 5, is thus practically equal to the mean value of the voltage of the tappings 3 and 3 Now the contact 9 is moved to the tapping .s and the contact l5 opened, I4 closed and it opened. By this the tapping 3 over the resistance 12 is connected with the winding 5 and then the resistance I2 is shortcircuited so that the tapping 3 is directly connected with the winding 5 by closing the switch I3, and then the switch 14 is opened and also the contact it moved up to the tapping 3 In this way the winding 5 successively is connected with the different tappings of the potentiometer -2, but each time with interconnection of the windings I and 8. When the voltage impressed upon the winding 5 shall be lowered the procedure is the opposite.

Instead of designing the coils 1 and 8 as above mentioned so that they will deliver half of the voltage difference between the tappings on the potentiometer, they may of course also be so dimensioned that they only deliver a third of this voltage difference but are then in the same or the opposite direction as the main voltage inserted in series with the transformer winding 5. The switch H will then of course be otherwise designed, because it must then serve for a reversing of the coils I and 8.

In spite of the fact that the invention in the first place is intended to be used for electric locomotives and described for such it may of course also be used in other cases, where a variation of a voltage shall be performed by a step regulation.

I claim as my invention:

1. In a voltage regulation system controlled by a. transformer having its secondary winding "connected with a load and its primary winding through a tap-changing device connec'table with a plurality of taps on an auto-transformer coupled to a source of alternating voltage, an additional winding wound on the primary side of the transformer, said additional winding having such a size as to deliver an additional voltage with a fraction of the voltage difference between the succeeding taps and also bein connectable by said tap-changing device with said taps for successive interconnection of said additional winding to the individual proceeding taps prior to the connection of the primary winding of the transformer therewith.

2. A system according to claim 1, wherein the additional winding comprises two parts connected in series, one of which is wound on the auto-transformer and the other is wound on the primary side of the transformer.

3. A system according to claim 1, wherein the additional windin has such a size as to deliver an additional voltage of substantially one-half the voltage difference between successive taps.

NILS sJoBERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,764,376 Whittaker June 17, 1930 2,200,083 Hibbard et a1. May 7, 1940 2,369,997 Baston Feb. 20, 1945 2,417,754 Hibbard Mar. 18, 1947 FOREIGN PATENTS Number Country Date 200,457 Switzerland Dec. 16, 1938 

